Texinfo is a documentation system that uses a single source file to produce both online information and printed output. It is primarily designed for writing software manuals.
For a full description of the Texinfo language and associated tools, please see the Texinfo manual (written in Texinfo itself). Most likely, running this command from your shell:
or this key sequence from inside Emacs:
M-x info RET m texinfo RET
lib/main.php:944: Notice: PageInfo: Cannot find action page